1. Field of the Invention
The present invention generally relates to a terminal, a semiconductor device, a terminal forming method and a flip chip semiconductor device manufacturing method, and more particularly to a terminal having a metal post, a semiconductor device, a terminal forming method and a flip chip semiconductor device manufacturing method.
2. Description of the Related Art
Recently, increasing density of semiconductor devices has promoted the development of technologies for reducing the size and the thickness of the semiconductor devices. Among the technologies, a flip chip bonding method is known as one of flip chip mounting methods for directly mounting a bare chip on a substrate.
A description will now be given, with reference to FIGS. 1A through 1C, of an outline of a conventional flip chip bonding method. In the flip chip bonding method, electrodes (pads) 21 through 25 are provided on an active surface of an electric element 3 such as an IC (Integrated Circuit) chip, CSP (Chip Size Package) and a SAW (Surface Acoustic Wave) filter as shown in FIG. 1A. Then, bumps 11 through 15 are formed as projection electrodes on the electrodes 21 through 25. As is shown in FIG. 1B, the electrodes 21 through 25 on the electric element 3 are aligned with electrodes 41 and 45 on a substrate 5 formed of ceramics or the like. After that, as is shown in FIG. 1C, the electrodes 21 through 25 on the electric element 3 are mounted to the electrodes 41 and 45 on the substrate 5 via bumps 6 by adding heat, pressure or the like. Here, the cylindrical bumps 6 are formed through surface tension between the electrodes 21 through 25 on the electric substrate 3 and the electrodes 41 and 45 on the substrate 5 by melting the spherical bumps 1. The bumps 6 may be formed as fillet-shaped bumps or barrel-shaped bumps instead of the cylindrical bumps.
There are some bump forming methods such as a plating method, a deposition method, a transfer method and a wire bonding method. In the wire bonding method, a bump, which is called a bonding bump, is formed by using a capillary of a wire bonding apparatus. Among these bump forming methods, the plating method and the wire bonding method are widely used because the deposition method and the transfer method include many processes and require large amounts of capital investment.
A description will now be given, with reference to FIG. 2, of a bonding bump formed according to the conventional bonding bump method. In FIG. 2, a bonding bump is provided on an electrode 12 on an electric element 11 and is formed of metal materials such as gold, copper and solder. The bonding bump comprises a bump part 13 and a neck part 14. For instance, the total height of the bump part 13 and the neck part 14 is about 50 μm through 60 μm.
A description will now be given, with reference to FIGS. 3A through 3D, of the conventional bonding bump forming method. In FIGS. 3A through 3D, a capillary 22 is often used in ordinary wire bonding methods. A wire 21 is extruded every predetermined length from the interior of the capillary 22. A ball 23 is formed at an end of the wire 21. An electrode 24 is provided on an electric element 25. A bump 26 is formed on the electrode 24.
The bump 26 is formed according to the following steps. First, as is shown in FIG. 3A, the ball 23 is formed at the end of the wire 21 by adding heat or providing a spark. Then, as is shown in FIG. 3B, the capillary 22 depresses and bonds the ball 23 on the electrode 24 in thermocompression by using an ultrasonic wave. As is shown in FIGS. 3C and 3D, when the capillary 22 is pulled up and the wire 21 is cut off, the bump 26 is formed on the surface of the electric element 25. If the above-mentioned steps are iterated, a large number of the bumps 26 can be formed on the surface of the electric element 25.
In the flip chip mounting, if a child chip is already mounted to the semiconductor device, it is necessary to provide a bump of appropriate height for successful implementation of the flip chip mounting without harmful influence on the chip.
In order to form such a bump of appropriate height, Japanese Laid-Open Patent Applications No. 08-162491, No. 08-264540 and No. 09-167771 disclose bump forming methods for forming a two-layer bump. In the bump forming methods according to Japanese Laid-Open Patent Applications No. 08-162491 and No. 08-264540, both layers of the two-layer bump are formed as bonding bumps. On the other hand, in the bump forming method according to Japanese Laid-Open Patent Application No. 09-167771, the two-layer bump has a plating bump in the lower layer and a bonding bump in the upper layer.
It is noted that the bump forming method according to Japanese Laid-Open Patent Application No. 09-167771 further can form more than two layers of a bonding bump so as to attain appropriate height.
In the disclosed conventional bump forming methods, however, a bonding bump method is used to form such a bump.
According to Japanese Laid-Open Patent Applications No. 08-162491 and No. 08-264540, since an ultrasonic wave is used in the conventional bonding bump method, the bump forming methods have a problem in that the ultrasonic wave is provided to an electrode two consecutive times so as to form a two-layer bump and an electrode under the formed two-layer bump is badly damaged due to the radiated ultrasonic wave.
Also, according to Japanese Laid-Open Patent Application No. 09-167771, although a multi-layer bonding bump of appropriate height can be formed, it is difficult to accurately superpose individual layers at the center of the bump. In general, the superposed layers are misaligned with respect to the center of the bump. In this case, it is impossible to obtain a proper flip chip connection due to connection misalignment.
Furthermore, it is difficult to control the height of a bonding bump in multi-layer bonding bump formation. As a result, it is impossible to form bonding bumps of uniform height, and there arises a difference between a high bonding bump and a low bonding bump. In this case, it is impossible to obtain a proper flip chip connection at the low bonding bump.